A Kinetic Analysis of the Ground Leg During Sprint Running

Abstract

Fifteen highly skilled sprinters were filmed while running at maximum velocity. The results were digitized and computer processed with interest focused on the muscle moments generated about the hip, knee, and ankle of the ground leg. Muscle activity about the hip consisted of extensor (concentric) dominance from foot descent, through foot strike, and into mid-support. Muscle dominance shifted to the hip flexors (eccentric) during mid-support and continued through takeoff. Muscle dominance at the knee demonstrated a pattern of flexor (eccentric, then concentric) dominance from foot descent through foot strike and into mid-support. Knee extensors (eccentric, then concentric) then achieved dominance through takeoff. During the later stages of takeoff, the dominance decreased or reversed briefly to flexor (eccentric) activity prior to a period of minimal activity following the toe-off position. From a period of minimal activity prior and subsequent to ground contact, the plantar flexors (eccentric, then concentric) of the foot were dominant throughout the ground phase. Qualitatively, the unexpected knee flexor dominance during foot strike was generated to limit the braking action created during this portion of ground contact. The unanticipated hip flexor dominance during takeoff served to rotate the upper body forward and into the approaching air phase. In addition, both of these actions allowed efficient use of the two-joint muscles of the leg during the critical phases of ground contact. Finally, the minimizing or reversing of the knee extensor dominance during the later stages of takeoff served to protect the joint from injury. Quantitatively, the magnitude of hip extensor/knee flexor activity during foot strike was significantly related (r = .70, p = .01) to the prior occurrences of related leg injury in the subjects.     

Longitudinal prediction and prevention of early reading difficulty

The results of many studies suggest that early reading problems are associated with deficiencies in certain spoken language skills. Children who encounter reading difficulty tend to be deficient in the perception of spoken words, the ability to retain linguistic material in temporary memory, and the ability to comprehend certain spoken sentences, as well as in their awareness about the phonological structure of spoken words. This paper summarizes these findings and provides an explanation in terms of the requirements of skilled reading. It further reviews the results of two longitudinal studies which show that inferior performance in kindergarten tests of language skills may presage future reading problems in the first grade. Based on these studies, procedures are suggested for kindergarten screening and for some ways of aiding children who, by virtue of inferior performance on the screening tests, might be considered at risk for early reading difficulties. Presented at the 33rd Annual Conference of The Orton Dyslexia Society, San Diego, California, November 1983. This paper was prepared while the author was a Fulbright Fellow at the Research Institute of Logopedics and Phoniatrics at the University of Tokyo, Tokyo, Japan. Much of the research herein described was supported by NICHD Grant HD-01994 and BRS Grant 05596 to Haskins Laboratories, Inc.     

浅谈大学数学课堂纪律建设

搞好大学数学课堂纪律建设,充分彰显课堂教学功效,既能更好地发挥学生的个性,又有助于教师更有效地管理课堂;既能让学生上课感到轻松,又可以很好地维护教师的尊严。     

Introduction to special issue on morphology and the acquisition of alphabetic writing systems

Reading and Writing -     

Evidence in seconds? Format and design considerations in the provision of reliable information to support evidence‐based practice

Evidence‐based practice is gaining support amongst health professionals. However, the major barrier remains the lack of time to read the literature. There are also problems with the take‐up and use of evidence‐based information sources such as Cochrane reviews and Effective Health Care bulletins. If such evidence is to be incorporated into local guidelines and used in day‐to‐day practice, practitioners request that these and other reliable publications be further summarized in short packages and available within seconds. The Health Evidence Bulletins Wales offer a model for this approach. The Bulletins have gone through several developmental stages leading to a novel two‐column format. In the first column, brief statements summarize the best available evidence within a topic area. In the second, full details are provided of the supporting publications (and the evidence type, or research design) with links to the full text of documents, where possible from the electronic versions of each Bulletin. Results from a questionnaire study using a random sample and unsolicited feedback suggest that this ‘two‐tier’ approach to information provision is valued by users and has implications for information services currently under development to support clinical governance.     

过程的完美与价值的回归--教学标准的构建是学校体育价值的回归

学校体育是教育系统的重要组成部分,建构理论与实践相结合的学校体育结构,是长期以来学校体育改革面临的严肃、认真的研究问题。学校体育要求教学从竞技化转向素质教育为核心。然而,在实际操作中缺乏理论的指导,教学过程缺失准确的定位。把学校体育标准构建纳入教学之中,确立切实可行的体育标准,实现学校体育真正意义上的“以人为本”。